A great many methods are known for constructing such a barrier wall, of which those most in use will be briefly described hereinafter.
A first known method consists in excavating a trench by means of an excavator provided with a chain having excavator buckets running about two guide rollers disposed vertically one above the other. During excavation, the chain is driven in a direction of travel and is simultaneously displaced in a horizontal direction. The trench excavated by the excavator is filled with a supporting fluid, e.g. bentonite, directly behind the excavator. Such a method is described in U.S. Pat. No. 4,379,658.
This method has the drawback that the depth of the trench is limited by the vertical height of the excavator and this is limited for practical reasons to about 10 meters. The width of the excavated trench is about 50 cm. The bentonite consumption, in view of this width, is substantial.
Another method of making a deep trench consists in providing juxtaposed wells by means of a hydrocutter, allowing to dig wells down to a large depth of as much as 200 meters. The cutter has a width of about 50 to 60 cm and a length of about 3 meters. The excavating method comprises making a first well, subsequently a second well at a distance slightly smaller the length of the cutter, after which the soil material remaining between the two wells is removed. The hydrocutter is adapted to operate in a bentonite fluid column, so that there is no danger that the wells cave in during the excavation. Such a method of constructing a deep trench is described in the non-prepublished Dutch patent application No. 87.02430.
Although the hydrocutter is adapted to operate down to a depth of about 200 meters, the trenches dug therewith cannot be deeper in practice than about 50 meters, because at a larger depth, the lateral deviation of the cutter may become too large. When two excavated juxtaposed wells exhibit opposite, lateral deviations, it can no longer be ensured that the panels excavated with the hydrocutter are continuous, which is necessary to form a continuous wall. Due to the width of the trench of 50 to 60 cm, the bentonite consumption in this excavating method, too, is substantial.
A third known method of excavating a deep trench consists in vibro-driving H-beams into the ground in juxtaposed relationship, while simultaneously injecting a bentonitecement slurry into the hole thus formed. The depth of the trench is limited to about 20-35 meters, since at larger depths it is no longer certain that the panels successively formed are continuous. The width of the trench may be considerably narrower than the above indicated width of 50-60 cm, so that in the last method, the consumption of supporting fluid is substantially less (U.S. Pat. No. 4,249,836).